Experimental investigations on stream-wise and span-wise orientations of wavy absorber plates and mesh in double pass solar air heater

Conventional stream-wise designs in porous mesh geometry exhibit limited solid–fluid thermal interaction, resulting in reduced thermal and fluid dynamic performance in double pass solar air heaters (DPSAH). To address the improvements in this, experimental investigations were conducted on span-wise configuration which is an alternative improved design and stream wise configuration. This study introduces a novel absorber plate and porous mesh combination in a span-wise configuration, explored experimentally for the first time. Experiments were performed for both the configurations at flow rates ranging from 0.025 kg/s to 0.055 kg/s and incident heat fluxes between 300 W/m² and 900 W/m². Results indicate that the span-wise configuration achieves 11.9 % and 15.1 % higher mean temperature differences of the fluid at flow rates of 0.025 kg/s and 0.055 kg/s, respectively. Mean Nusselt number increases with Reynolds number, with the span-wise configuration showing superior performance. Reduction in pressure drop 50 % to 60 % is observed in the span-wise configuration, contributing to improved energy savings. At highest incident heat flux of 900 W/m², the friction factor in the stream-wise configuration is 1.8 times and 3.45 times higher at 0.055 kg/s and 0.025 kg/s, respectively demonstrating greater energy losses in it than latter. Span-wise configuration exhibited maximum second law efficiency improvement of 20.9 % at Re of 5531 with 900 W/m². Additionally, annual cost savings of 7.6 % is achieved in span-wise configuration. Span-wise configuration exhibits improved thermal efficiency and overall performance index across all the conditions, making it promising for enhanced heat transfer, reduced fluid friction, and improved energy savings.